**2. Lactic acid bacteria**

The term lactic acid bacteria refers to a taxonomically diverse group of Gram-positive bacteria, facultative anaerobic, nonspore-forming, nonmotile, and acid-tolerant cocci, coccobacilli, or rods that appear as single cells or forming couples, tetrads, or long chains, with common metabolism and physiology capable of fermenting sugars primarily into lactic acid. LAB species are found in two phyla, the *Firmicutes* and the *Actinobacteria*; for the first the genus, *Aerococcus*, *Alloiococcus*, *Carnobacterium*, *Enterococcus*, *Lactobacillus*, *Leuconostoc*, *Oenococcus*, *Pediococcus*, *Streptococcus*, *Tetragenococcus*, *Vagococcus*, and *Weissella* that are low G + C (31–49%) belong to the *Bacilli class* and the *Lactobacillales* order. While, the *Bifidobacterium* genus with a high G + C content (58–61%) belongs to the *Actinobacteria* phylum [6, 14, 15].

This bacterial group is classified into homofermentative and heterofermentative according to the end products derived from the glucose metabolism. The homofermentative converts glucose mainly into lactic acid by the Embden-Meyerhof pathway, while the heterofermentative LAB transforms glucose into lactic acid, carbon dioxide, and ethanol or acetic acid by the 6-phosphogluconate pathway. LAB are capable of inhibiting the growth of spoilage and pathogenic bacteria based on the competition for nutrients and adhesion niches due to their great acid tolerance and ability to adapt to redox changes [14, 15]. In addition LAB are capable to produce antimicrobial metabolites such as lactic and acetic acids, ethanol, hydrogen peroxide, diacetyl, antifungals (short-chain fatty acids derived from lipolysis reactions), antimicrobial peptides known as bacteriocins, and other antibacterial proteins like peptidoglycan hydrolases (PGH) capable to cleave the peptidoglycan cell wall of Gram-positive and Gram-negative bacteria [6, 14]. Bacteriocins are ribosomal antimicrobial peptides active against closely related and non-related sensitive bacterial strains by forming pores in the cytoplasmic membrane and responsible for the reduction of microbial LAB competitors under stress conditions. Several studies have demonstrated the potential of bacteriocins to be applied for food preservation and in the pharmaceutical industry for their action against spoilage microorganisms and pathogens such *Listeria monocytogenes* and *Staphylococcus aureus* [16–18].

transmissible to pathogens through the food chain [3, 6]. The resistance to a specific antimicrobial may be intrinsic (when a microorganism does not possess target sites for the antimicrobial) or acquired. The acquired resistance is more complex and involves the presence of enzymes that inactivate the antimicrobial, posttranscriptional, or posttranslational modifications of the target site or reduction uptake and active efflux of the antimicrobial; those mechanisms derive from the gain of exogenous DNA or the mutation of indigenous DNA [4, 9, 10]. In general the AR genes can be horizontally transferred from one microorganism to another by transduction (via bacteriophages) or by transformation between microorganisms (when released DNA is taken up by other microorganism). However, it is claimed that the primary mechanism to acquire resistant is by direct cell to cell contact or conjugation between different genera of bacteria, especially when the resistant genes are present on mobile genetic elements such as plasmids and transposons [5, 10, 11]. LAB are highly adaptable and capable of developing resistance to antibiotics; most AR studies were focused on pathogenic microorganisms, but recently some investigators have questioned the safety of commensal LAB as some strains of *Lactococcus lactis*, *Enterococci*, and *Lactobacillus* isolated from fermented foods showed genes

Bacterial resistance to antibiotics is an emerging public concern that may compromise the efficacy of agents used for the treatment of infectious diseases [13]. Therefore, the objective of this chapter is to present an overview of the LAB antibiotic resistance and some methods to determine this characteristic, as per the FAO/OMS guideline for testing food-related bacteria

The term lactic acid bacteria refers to a taxonomically diverse group of Gram-positive bacteria, facultative anaerobic, nonspore-forming, nonmotile, and acid-tolerant cocci, coccobacilli, or rods that appear as single cells or forming couples, tetrads, or long chains, with common metabolism and physiology capable of fermenting sugars primarily into lactic acid. LAB species are found in two phyla, the *Firmicutes* and the *Actinobacteria*; for the first the genus, *Aerococcus*, *Alloiococcus*, *Carnobacterium*, *Enterococcus*, *Lactobacillus*, *Leuconostoc*, *Oenococcus*, *Pediococcus*, *Streptococcus*, *Tetragenococcus*, *Vagococcus*, and *Weissella* that are low G + C (31–49%) belong to the *Bacilli class* and the *Lactobacillales* order. While, the *Bifidobacterium* genus with a

This bacterial group is classified into homofermentative and heterofermentative according to the end products derived from the glucose metabolism. The homofermentative converts glucose mainly into lactic acid by the Embden-Meyerhof pathway, while the heterofermentative LAB transforms glucose into lactic acid, carbon dioxide, and ethanol or acetic acid by the 6-phosphogluconate pathway. LAB are capable of inhibiting the growth of spoilage and pathogenic bacteria based on the competition for nutrients and adhesion niches due to their great acid tolerance and ability to adapt to redox changes [14, 15]. In addition LAB are capable to produce antimicrobial metabolites such as lactic and acetic acids, ethanol, hydrogen peroxide, diacetyl, antifungals (short-chain fatty acids derived from lipolysis reactions), antimicrobial

high G + C content (58–61%) belongs to the *Actinobacteria* phylum [6, 14, 15].

conferring resistance to tetracycline, erythromycin, and vancomycin [12].

and probiotics for resistance patterns.

**2. Lactic acid bacteria**

56 Antimicrobial Resistance - A Global Threat

LAB have been safely used for centuries in numerous indigenous food fermentations up to the actual modern industry in the elaboration processes for dairy products, vegetables, meats, coffee, cocoa, silages, sourdough bread, and wine, as LAB contribute to the taste, flavor, and texture of those fermented products but also inhibit the development of spoilage and pathogenic microorganism by acidification and production of antimicrobials [14, 19]. Therefore, LAB are widely employed as starter cultures in the food industry to accelerate ripening or to control the adventitious microbiota for elaboration and preservation of several fermented foods including dairy (hard- and semihard-type cheeses, yogurt, butter, and cream), meats, sourdough bread, and vegetables. LAB contribute to the taste, flavor, and texture of those fermented products as a result of several reactions, including lipolysis, proteolysis, and conversion of lactose in citrate and pyruvate intermediates that can be converted to various aromatic compounds, such as diacetyl, acetoin, acetaldehyde, and acetic acid. Proteolytic processes induces the accumulation of small peptides and free amino acids that are further transformed into alcohols, aldehydes, acids, and esters responsible for the flavor profile and organoleptic characteristics of fermented foods [14]. In addition some LAB strains such as *Lactococcus lactis*, *Lactobacillus sakei*, *Lactobacillus rhamnosus*, *Lactobacillus helveticus*, and *Streptococcus thermophilus* can produce exopolysaccharides (EPS) that not only confer protection to the cell producer but can be applied in the food industry as thickeners to increase viscosity and firmness, improving texture and mouthfeel of yogurt and other low-fat milk products. The EPS produced by LAB range from 10 to >2000 kDa and can be classified as homo- or heteropolysaccharides according to their monomer composition, where galactose, glucose, and rhamnose are the most common monomers [20].

Some LAB are present in the respiratory, gastrointestinal, and genital tracts of humans and animals and therefore used as probiotics for healthiness improvement related to their influence on the immune system for the prevention and control of some infections during pregnancy or as part of the treatment for antibiotic-derived diarrhea, constipation, and intestinal inflammation, also to manage allergies and lactose intolerance and prevention of urinary infections [21–23]. The WHO and FAO describe the probiotics as live microorganisms that in adequate amounts confer health benefits for the host [24]. Several strains of *Lactoccocus*, *Lactobacillus*, *Streptococcus*, *Enterococcus*, *Bifidobacterium*, *Pediococcus*, and *Propionibacteria* present in foods and in dietary supplements are commonly used as probiotics and considered desirable members of the intestinal microbiota that can be used to deliver vaccines and other metabolites directly in the gastrointestinal tract [21]. Consumption of LAB probiotics may help for modulation of the immune system and reduction of pathogens, thereby, improving the gut functionality. Other health benefits associated to the consumption of LAB probiotics include an antihypertensive effect, reduction in the serum cholesterol level, antioxidant effect, protection against colon cancer, reduction in the allergy symptoms, reduction in dental caries, and reduction in the obesity index [21, 22]. In addition, secondary metabolites with health-promoting properties include the antihypertensive angiotensin-converting enzyme produced through the proteolytic system of *Lactobacillus helveticus*, *Lactobacillus acidophilus*, and *Lactobacillus delbrueckii* [14, 22].

promoters or pathogen inhibitors, is directly related to the presence of AR microbiota in the human gastrointestinal tract [27, 32]. On the other hand, Gad et al. [21] isolated some *Lactobacillus*, *Streptococcus*, and *Lactococcus* strains from both pharmaceutical and probiotic dairy products, but the AR tests from the pharmaceutical probiotic isolates were free of resistance genes, unlike the LAB isolated from dairy products that showed resistance profiles comparable to those from pathogens such as *Staphylococcus spp*., *Escherichia coli*, and *Salmonella spp*. Furthermore, some *Enterococcus faecium* strains have demonstrated the transference of vancomycin resistant genes

Antibiotic Resistance in Lactic Acid Bacteria http://dx.doi.org/10.5772/intechopen.80624 59

from to *Lactobacillus acidophilus* La5 "in vitro" and "in vivo" studies in the gut mice [33].

elements such as plasmids or transposons [12, 19, 28].

**3.1. Mechanisms of resistance in LAB**

through the action of efflux pumps [34, 35].

pumps or due to the change in the cell wall permeability [19].

Exposure to antibiotics may allow bacteria to develop different mechanisms to counteract the bactericidal effect; a single bacterium can develop different types of resistance; these systems include an intrinsic or innate and the acquired resistance mode. Among these, the mechanism that prevails within bacteria varies according to the nature of the antibiotic, the target site, the bacterial species, and/or whether the resistance gene is part of the chromosome or mobile

Two relevant elements must be present for the antibiotic-target interaction, first the antibiotic must recognize the target, and the concentration of the antibiotic in the target must be sufficient to inhibit the bacterial growth. A resistance mechanism conduces to the antibiotic failure to inhibit the bacterial growth due to an inefficient antibiotic-target interaction, which can be classified as passive and active. The passive mechanism can only be transferred to other cells by clonal transfer that involves modifications of the target site or decrease in antimicrobial absorption, without affecting the antibiotic structure; this resistance is also known as intrinsic resistance. In contrast, the active mechanism involves the reduction on the concentration of the intracellular antibiotic by modification or degradation of its structure with enzymes or

**Figure 1** shows the mechanisms by which some bacteria can show resistance to antibiotics that involves (1) modification of the antibiotic by enzymatic complexes that prevent the antibiotic-target interaction, (2) enzymatic degradation of intra- or extracellular antibiotics, and (3) reduction in the intracellular antibiotic concentration through the activation of flow

The main mechanism of resistance to antibiotics presented by LAB has been related with multidrug-resistant (MDR) efflux pumps involved in the expulsion of structurally unrelated compounds [31, 36]. Wacher-Rodarte et al. [37] analyzed LAB isolated from pozol (a traditional fermented maize beverage), identifying that MDR strains such as *Lactococcus lactis* and *Lactobacillus plantarum* present active efflux pumps, including the chromosomally encoded ABC type with the LmrA transporter (*lmrA* gene). On the other hand, Poelarends et al. [38] demonstrated that the presence of the LmrA transporter in *Lactococcus lactis* is associated with the innate resistance of 17 up to 21 clinically relevant antibiotics, including aminoglycosides (kanamycin and gentamicin), lincosamines (clindamycin), macrolides (erythromycin), quinolones (ciprofloxacin), and tetracyclines. Other authors such as Casado Muñoz et al. [39] reported that *Lactobacillus pentosus* and *Leuconostoc pseudomesenteroides* isolated from fermented olives are resistant to cephalosporins, streptomycin, and kanamycin due to the

LAB are considered naturally resistant to several antibiotics and may have the potential to acquire resistance to other antimicrobials or to disseminate the resistance to pathogens present in the gastrointestinal tract of animals and humans [9]. For instance, Shao et al. [11] demonstrated that two isolates of *L. plantarum* possessed the *aaad*A and *ant*(6) genes associated to the resistance to streptomycin, and the overexposure to this antibiotic dramatically increased the minimum inhibitory concentration (MIC) and increased a cross-resistance to other antibiotics from the same class. On the other hand, the presence of 6% strains isolated from some pharmaceutical and dairy products from Egypt with tetracycline [*tet*(M)] and/ or erythromycin [*erm*(B)] resistant genes has been reported [21]. In a similar study, a high incidence of *Lactobacillus* resistant to vancomycin (58%), erythromycin (10.8%), tetracycline (4.3%), gentamicin (48%), and ciprofloxacin (26%) was reported in Turkish fermented dairy products [13]. However, studies made by Flores and Mayo [25] indicate that no transfer of the tetracycline [*tet*(M)] and erythromycin [*erm*(B)] resistant genes from *S. thermophilus* to *L. delbrueckii* was detected during the production and storage of yogurt. Furthermore, the food chain can facilitate the transmission of antibiotic-resistant bacteria between animals, foods, and humans, being the fermented milk and meat products the most common vehicle for antibiotic-resistant bacteria to the indigenous flora of the gastrointestinal tract, as these products are consumed without a thermal treatment [12]. Even though that some reports confirm the transmission of resistant determinants, the two most common resistant genes in LAB are tetracycline [*tet*(M)] and erithromycin [*erm*(B)] resistant genes, followed by *cat* genes coding for chloramphenicol resistance [26]. Considering the wide range of potential applications of LAB in the industry and in the human and animal health, there is a need of their detailed examination that involves the detection of AR genes.
